1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for implementing improved frequency estimation for wireless communications in support of a broader set of use cases including outdoor use cases and use cases that involve lower power transmissions with reduced signal-to-noise ratios for receivers particularly in systems configured according to the pending IEEE 802.11ah standard.
2. Related Art
The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards are a set of standards and revisions of those standards for implementing wireless local area network (WLAN) or Wi-Fi communications, principally in the unlicensed 2.4 and 5 GHz frequency bands. IEEE 802.11 standard communications are often broadly characterized as encompassing a series of half-duplex over-the-air modulation techniques, all of which employ a same basic protocol. The original version of the IEEE 802.11 standard was released in 1997, but has been superseded by later versions that have re-defined and/or clarified these wireless communications standards. The later versions address evolution of the particular wireless communication implementations and use cases covered by the expanding use of the designated portions for the unlicensed communication spectrum.
Arguably, the most well known and prolific versions of the standards to date are the IEEE 802.11b (released September 1999), 802.11g (released June 2003) and 802.11n (released October 2009) standards, each of which is an amendment to the original standard. The IEEE 802.11b and IEEE 802.11g standards are directed to devices that use the 2.4 GHz band, while the IEEE 802.11n standard, which improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO), operates on both the 2.4 GHz and the lesser used 5 GHz bands. The IEEE 802.11ac (Pending, draft released November 2011) standard is a next generation wireless computer networking standard in the IEEE 802.11 series. The IEEE 802.11ac standard is currently under development and is expected to provide standards for systems and devices that support high-throughput WLAN communications in the 5 GHz band. The pending IEEE 802.11ac standard is anticipated to enable multi-station WLAN throughput of at least 1 Gb/sec, with improvements over IEEE 802.11n.
WLAN or Wi-Fi communications and use cases for those communications continue to evolve. The use cases and environments for those communications are broadening tremendously from the original home/office or wireless hotspot Internet access to additional use cases that include communications that support high volume entertainment streaming to communications with myriad sensor networks. This last use case poses some unique challenges in meeting certain unique requirements. In order to address these unique aspects, another IEEE 802.11 standard, IEEE 802.11ah (Pending) is separately under development.
As indicated above, WLAN and Wi-Fi communications are well standardized for the 2.4 and 5 GHz frequency ranges. There are, however, some number of non-standard modified WLAN and Wi-Fi devices available that are configured to operate in a sub-1 GHz frequency range. Vendors often take the core technology and change the frequencies at which the devices operate. A demand for such devices has emerged, in part from the smart grid community, to link to smart meters because of the potential for greater range outdoor communications for a same power out with lower obstruction losses, or alternatively to maintain communications ranges indoor with lower power transmitters associated with, for example, arrays of indoor sensors. In an effort to combat a lack of interoperability with each vendor providing its own proprietary implementation, potentially tying groups of smart grid customers separately to individual vendor implementations, the IEEE commenced the efforts to amend the 802.11 standard to include sub 1 GHz operations. These efforts on the part of the IEEE are consolidated in a Working Group developing the new IEEE 802.11ah standard. This standard will, among other objectives, establish standard RF channel widths and center frequencies for the sub 1 GHz frequency operations and devices. The IEEE 802.11ah standard is being crafted to accommodate ultra-low-power specification devices operating in the sub-1 GHz range, which would imply a much wider range than the 2.4-GHz IEEE 802.11n or 5.0-GHz IEEE 802.11ac technologies.
The IEEE 802.11ah standard systems are being developed to reuse, as much as possible, the IEEE 802.11ac system design. As the specifics of the IEEE 802.11ah standard emerge, it becomes clear that systems operating according to the IEEE 802.11ah standard will employ bandwidths including a new 1 MHz bandwidth that will uniquely supplement a set of down-clocked IEEE 802.11ac standard rates, namely 2, 4, 8 and 16 MHz, where the down-clocking is 10×. The 1 MHz rate is not derived from the IEEE 802.11n or IEEE 802.11ac standard rates. Thus, the 1 MHz bandwidth mode is being designed relatively independently. The 1 MHz system is anticipated to use a new32 point Fast Fourier Transform (FFT), as opposed to the minimum 64 point FFT used in the IEEE 802.11ac standard. The 2, 4, 8 and 16 MHz bandwidths will have a preamble structure like that of the IEEE 802.11ac standard. The 1 MHz system of the IEEE 802.11ah standard will use a similar preamble structure, but will include repetition in the preamble to allow the 1 MHz system to reach further in range, or to operate at lower power.